1. Field of the Invention
The present invention relates to a hoist clamp and is concerned particularly with such a clamp for lifting and turning loads and having a casing with a load aperture, a movable and a fixed clamp whereby the movable lever-like clamp is acted upon by arms driven by an eye coupling moved by a universal joint and whereby, in the event of a diagonally exerted pull, the eye coupling is braced against the casing in order, by means of lever action, to increase the clamping force in the clamp.
2. Description of the Prior Art
German reference DE-PS No. 24 53 121 discloses a clamp of the above-mentioned type. The eye coupling is linked to an arm arrangement by a universal joint. The arm arrangement acts on the movable jaw of the clamp. If a diagonal pull is now exerted on the eye coupling, the eye coupling braces itself against the hoist clamp casing, thereby producing a lever action which causes the clamping force between the clamps to increase thereby at least partially compensating for loss of clamping force due to the diagonal direction of the pull.
With a hoist clamp of the type just described the height of the universal joint relative to the parts of the casing against which the eye coupling is braced when a diagonal pull is exerted, depends on the thickness of the load clamped in the jaws of the hoist clamp. If loads are thick, the universal joint with its two shafts is in a lower position, whereas, with slender loads, the universal joint is lifted and pulled clear of the clamp hoist casing.
As a consequence of the difference in height of the universal joint, it is possible to determine beforehand at which point the eye coupling will brace itself against the casing of the hoist clamp. A further consequence is that a case may arise in which the elements of the eye coupling which act in conjunction with the bracing points on the casing lose contact with the casing with the result that, in the case for example, of a slender load, it is not possible to gain sufficient, if any, increase in the clamping force.
However, known devices of this kind rely heavily on the thickness of the load for their effect and as a consequence use an unsafe method of operation in the case of the hoist clamp when loads vary greatly or when different diagonal pulls exerted.
German Patent Specification DE-PS No. 22 55 629 describes a hoist clamp where the movable clamp jaw is connected to an eye coupling by means of a rope which passes over reversing pulleys. From this design it is quite clear that is is possible to produce identical clamping forces even when the direction of pull is diagonal, regardless of the size of the load. Nevertheless, a rope can only be used for special purposes since thick wire ropes will not reverse sufficiently.
The disadvantage caused by the size of the load can be overcome by designing an adjustable fixed clamp. However, a design of this kind demands careful operation which cannot always be guaranteed and which requires additional effort and expense.